Condensation may occur on a surface of an object when its temperature drops below the dew point for the surrounding air. This effect may be observed in the formation of dew on grass, condensation of water droplets on a drinking glass, or fogging of a window or lens. In freezing conditions, condensation may accumulate on a surface of an object in the form of frost.
Such fogging or frosting may be undesirable on lens or other surface through which it is desirable to see or otherwise transmit light, for example, on the lens of a vehicle instrument gauge.